<html>
<head>
<style>
.square {
  margin: 25px;
  height: 60px;
  width: 60px;
  background-color: black;
}

.rounded {
  margin: 25px;
  height: 60px;
  width: 60px;
  background-color: black;
  border-radius: 30px;
}

#negative {
  -webkit-box-shadow: 110px 0px 0px -10px #00f,
                      260px 0px 0px -15px #00d, 
                      410px 0px 0px -20px #00b,
                      560px 0px 0px -25px #009;
}

#positive {
  -webkit-box-shadow: 110px 0px 0px  10px #00f,
                      260px 0px 0px  15px #00d, 
                      410px 0px 0px  20px #00b,
                      560px 0px 0px  25px #009;
}

</style>
</head>
<body>
<div class="square" id="negative"></div>
<div class="square" id="positive"></div>
<div class="rounded" id="negative"></div>
<div class="rounded" id="positive"></div>
</body>
</html>
